ore reserves and mineral resources 2011 report - Anglo American ...

SECURING OUR FUTURE
ORE RESERVES AND MINERAL RESOURCES
MINERAL RESOURCES
The platinum group metal (PGM) Mineral Resources of Anglo
American Platinum Limited (Amplats) occur almost exclusively
within southern Africa, and are hosted by two distinct but unique
ultramafic layered intrusions: the Bushveld Complex in South Africa
and the Great Dyke in Zimbabwe.
Total PGM Resources present within these two geological features
account for approximately 85% of the world’s known platinum and
55% of the world’s known palladium.
THE BUSHVELD COMPLEX
The Bushveld Complex is geologically unique owing to its size,
uniform layering and mineral content. Formed over two billion years
ago from multiple injections of molten magma into the earth’s crust
many kilometres below the earth’s surface, the resultant saucershaped
intrusion is over 350 kilometres wide, 250 kilometres long
and up to 12 kilometres thick. Over many millions of years the rim of
the intrusion has been exposed by erosion, revealing three separate
segments known as the Western, Eastern and Northern limbs
respectively. The exposed segments exhibit layering of different rock
types (such as pyroxenites, norites, gabbros and chromitites) and
this layering occurs across the entire extent of the complex. Within
the layers, mineralisation is found within specific horizons containing
economic minerals that host chromite, titanium, vanadium, nickel,
copper and, more importantly for Amplats, the platinum group
metals or PGMs.
Economic concentrations of PGMs occur within three distinct reefs
within the Bushveld Complex: the Merensky Reef, the Upper Group
2 (UG2) Chromitite and the Platreef. The Merensky Reef and the
UG2 Reef occur around the Eastern and Western limbs of the
complex, while the Platreef is found only along the eastern edge of
the Northern Limb.
The Merensky Reef and the UG2 Reef
The Merensky and UG2 reefs are narrow tabular orebodies that
extend laterally over hundreds of square kilometres, resulting in
extensive Mineral Resources. Their continuity, established over
years of exploration and mining, allows for long-range extrapolation
of data. The Merensky Reef has been the principal source of PGMs
since it was first mined in 1925. However, with the depletion of
shallow Merensky Resources the UG2 Reef, which is found at a
vertical distance of between 16 and 400 metres below the Merensky
Reef depending on the location, has grown steadily in importance to
the point where it now accounts for more than 50% of all the
platinum-bearing ore processed in South Africa.
The Platreef
On the Northern Limb of the Bushveld, the Merensky and UG2 reefs
are not developed on Amplats’ properties. However, the Platreef,
which is substantially thicker than either the Merensky Reef or the
UG2 Reef, is well developed. The Platreef was mined briefly in the
1920s, but has been exploited on a large scale only since 1993. It is
gradually becoming a significant contributor of PGMs for Amplats.
The term ‘Platreef’ describes zones of mineralisation occurring in a
variety of rocks that range from normal pyroxenites to calcsilicates
that have arisen through the contamination of Bushveld magma by
sediments from the underlying Transvaal Supergroup. In general,
the economic thickness of the Platreef is such that it can support
open-pit mining operations to depths well in excess of 200 metres at
current prices and mining costs.
Base metal mineralisation
The Merensky Reef and the Platreef yield meaningful quantities of
nickel and copper as by-products of PGMs, whereas the UG2 Reef is
relatively devoid of these metals. Although chromitite contained in
the UG2 has potential for economic gain and in some areas is being
exploited as a by-product, Amplats has not considered this when
measuring the reef’s contained monetary values for Ore Reserve
purposes. However, other UG2 base metals have been considered,
and their value has been accounted for in the relevant economic
evaluations.
THE GREAT DYKE
The Great Dyke is located in Zimbabwe and occurs as a major
intrusion that trends in a north-easterly direction and is over
500 kilometres in length. It comprises mafic and ultramafic rocks
that cut across the dominantly Achaean rocks of the Zimbabwe
Craton, consisting mostly of granite and greenstone belt rocks. PGM
and associated base metal mineralisation is developed within a
mafic/ultramafic horizon and covers over 720 square kilometres of
the Great Dyke.
4 ANGLO AMERICAN PLATINUM LIMITED 2011